# C++ 程序：顯示兩個間隔之間的質數 > 原文： [https://www.programiz.com/cpp-programming/examples/prime-number-intervals](https://www.programiz.com/cpp-programming/examples/prime-number-intervals) #### 在 C++ 編程中打印兩個數字（由用戶輸入）之間的所有質數的示例。 使用嵌套的`for`循環和`if...else`語句可以解決此問題。 要理解此示例，您應該了解以下 [C++ 編程](/cpp-programming "C++ tutorial")主題： * [C++ `if`，`if...else`和嵌套`if...else`](/cpp-programming/if-else) * [C++ `for`循環](/cpp-programming/for-loop) * [C++ `break`和`continue`語句](/cpp-programming/break-continue) * * * * * * ## 例 1：顯示兩個間隔之間的質數 ```cpp #include <iostream> using namespace std; int main() { int low, high, i, flag; cout << "Enter two numbers(intervals): "; cin >> low >> high; cout << "Prime numbers between " << low << " and " << high << " are: "; while (low < high) { flag = 0; for(i = 2; i <= low/2; ++i) { if(low % i == 0) { flag = 1; break; } } if (flag == 0) cout << low << " "; ++low; } return 0; } ``` **輸出** ```cpp Enter two numbers(intervals): 20 50 Prime numbers between 20 and 50 are: 23 29 31 37 41 43 47 ``` 在此程序中，`while`循環被迭代`(high - low - 1)`次。 在每次迭代中，檢查`low`是否是質數，然后將`low`的值增加 1，直到`low`等于`high`。 訪問此頁面以了解有關如何[檢查數字是否為質數](/cpp-programming/examples/prime-number "C check prime number")的更多信息。 如果用戶首先輸入較大的數字，則該程序無法正常工作。 如果用戶先輸入較大的數字，則可以通過[交換數字](/cpp-programming/examples/swapping "swap numbers in C programming")來解決此問題。 * * * ## 例 2：首先輸入較大的數字時顯示質數 ```cpp #include <iostream> using namespace std; int main() { int low, high, flag, temp; cout << "Enter two numbers(intevals): "; cin >> low >> high; //swapping numbers if low is greater than high if (low > high) { temp = low; low = high; high = temp; } cout << "Prime numbers between " << low << " and " << high << " are: "; while (low < high) { flag = 0; for(int i = 2; i <= low/2; ++i) { if(low % i == 0) { flag = 1; break; } } if (flag == 0) cout << low << " "; ++low; } return 0; } ``` 訪問此頁面以了解如何使用用戶定義的函數來[顯示兩個時間間隔之間的所有質數](/cpp-programming/examples/prime-interval-function)。